1. Field of the Invention
The present invention relates to generating a reference voltage in integrated circuits, and more particularly to reference voltage circuits for low-power applications.
2. Description of the Related Art
A bangap reference circuit has improved temperature stability and is less dependent on power supply voltage than other known voltage reference circuits. Bandgap reference circuits typically generate a reference voltage approximately equal to the bandgap voltage of silicon extrapolated to zero degrees Kelvin, i.e., VG0=1.205V. Typical voltage reference circuits include a current mirror coupled to the power supply and the voltage reference node to provide a current proportional to the absolute temperature to the voltage reference node.
Integrated circuits having 3V power supplies can easily meet the demands of operating devices included in a cascoded current mirror and generate the reference voltage without compromising stability of the reference voltage. For example, a voltage reference generator with a power supply of 3V provides a reference voltage of 1.2V. The VDS of a MOSFET included in the current mirror has a magnitude of 3V−1.2V=1.8V, which is sufficient to operate the device under typical conditions with an acceptable power supply rejection ratio (PSRR) (i.e., the ability of the voltage reference generator to reject noise on the power supply). However, as the power supply voltage drops, e.g., for low-power applications, available voltage headroom required to operate the devices included in the current mirror is reduced, the PSRR becomes more critical, and the voltage reference generator is less likely to provide a sufficiently stable reference voltage with respect to variations on the power supply.
Accordingly, improved techniques for generating stable reference voltages for low-power applications are desired.